Resistance device.



L. L H. I., BRADLEY.

RESISTANCE DEVICE. l

APPLIQATION FILED DEO.14, 1908.

, Patented Mar. 4, 1913.

FIG,

Lynderaaiey Harry LmdZejn llfzffzesses:

@Vm (Bggpxw.

STAT

L PATEN e LYNDE BRADLEY AND HBRY L. BRADLEY, 0F MUSKEGON, MICHIGAN, ASSIGNORS T0 ALLENfBBADLEY COMPANY, A. CORPORATION 0F WISCONSIN.

RESISTANCE DEVICE.

Specication of Letters Patent.

Patented Mar. 4, 1913..

Be it known that we, LYNDE BRADLEY and HARRY L. BRADLEY, citizens of the United States of America, and residents of Muskegon, county of Muskegon, -and State of Michigan, have invented a new and useful Improvement in Resistance Devices, of which the following is a speciiication.

Our invention pertains to resistance units.

I t relates particularly tot-hat class of variable-resistance units wherein a resistance component of variable resistance value is used, the resistor being composed of a numberof carbonaceous lates so arranged as to be compressed and) released in order to bring about the desired changes in the electrical resist-ance of the path through the` resistor.

The mechanism for compressing and releasing the resistor forms no part of the present invention, asuitable mechanism being shown for4 instance in Patent No. 821,697, May 29, 1906, for an electrical current controller. A method of and means for exerting and relieving the ressure on a column of disks is clearly in icated in that patent. Since our present invention relates to the variable-resistance unit, rather than to any means for'compressing the resistor thereof, `it is obvious that the variable-resistance unit of ourpresent invention may be made in any form 'and may be used with any type of compressor.

A diiliculty in the use of compressible variable resistance units heretofore hasl been lack of durability and constancy in the resistor. The best available compressible resistor heretofore known has been a column of amorphous carbon disks, but such disks thus used deteriorate. Under ordinary service through longperiods of time aldisintegration ci the carbon disks begins at the middle of the disks', or at the axis of. the column and grows outwardly, thus indicati ing that the disintegration is mechanical or allotropic rather than chemical, there being no chemical changes in the constituency of the material so far as we have been able to. determine, and not due to combustion or Oxidation, sul@ it Occurs ata place when" Oar-gen exists .very limite quantities. .or is entirely absent..

Qur rarement eifel; the prior art such. re @rsf arid. 15.93 in. the

provision of an improved resistor, an improved container or retainer for the resistor, and in the improved resistance unit result ing upon the assembling of those improved parts with other improved auxiliary parts to form a complete resistance unit.

The container for the variable resistance medium and the process by which it is made are made the subject matter of another application, Serial No. 535,223, filed December- 27, 1909, the present application relating particularly to the resistance element per se and the complete resistor unit.

In the drawings, Figure 1 shows an as.- sembled resistance unit of a type selected for speciiic illustration herein, the device being shown partly in section; Fig. 2 shows the tubular container forming a structural part of the variable-resistance device of Fig. 1, the wall of the container being shown in part in section; Fig. 3 shows a portion vof the wallof the container of Fig. 2, in section, on an enlarged scale; Fig. 4 shows sectional view of one of the heat-radiating ribs of Fig. l; Fig. 5 shows a detail of the upper terminal of the device of Fig. 1; and Fig. 6 shows a modified detail :tor devices .of the general type of Fig. 1.

.the radiating ribs 3. At the bottom the tube 2 is restricted so as to form a shoulder 28. This shoulder, as illustrated in Figs. 1 and 2, is made by drawing or spinning the metal of the tube toward the center line of the tube, and serves partially to close the end of the tube to form a seat for the copper-headed stud 4, which has its head within the tube and its shaft projecting through the opening in the bottom thereof. Upon the stud 4 the lower cap 5 is held by the nut 6 and its washer 7, the stud being insulated from the cap and tube by insulating washers-and" bushings. The nut 12 isl provided to clamp a leading-in conductor. The radiatingribs 34 are cut'in annular torni from sheet metal and the ,central lip is shaped up in a shaping press by stretching the metal. These are forced upon the outside of the tube 2 the central lip 3.." ora algae member acting to determine the distance between ribs and to maintain the alinement of the ribs. Upon the head of the stud 4 rests a copperplated graphite cylinder 13, the upper face being left unplated, and upon this part and Within the container 2` are piled the resistance disks 1, Which as a Whole make up the resistance element of the resistance unit. At the top of the series of resistance disks, a terminal is provided. A graphite disk 14 is laced in contact with the top resistance ilisk; upon the disk 14 is a copper-plated graphite cylinder 15, the under face being left unplated, Which is attached to terminal plug 16. The terminal plug 16 preferably is of aluminum to avoid excessive Weight which would tend to compress the resistor l. The flo-ating terminal plug 16 is connected electrically through the flexible copper conductor 17 to lthe bolt 18 and n ut 19, which are adapted to clamp the other leading-in conductor. Top cap 20 is clamped at 21, holding insulating bushing 22 in place and being further insulated by insulating Washer 23. The tube 2 is lined With an insulating lining 24 attached to the Wall of the tube by the layer of cement 25, the cement 25 being also an insulator, preferably.

The resistance medium, or resistor, which in the device of Fig. 1 is the column of disks l, is held by a metallic retainer, but'- is insulated from the metal. The insulating material used in connection With the retainer must possess great heat-resisting properties, must not crumble, flake off or loosen under changes in temperature, and also must be proof against undue deterioration by mechanical Wear, as there Will be more or less sliding of the resistor against the insulating Wall in the processes of compression and release of the resistor. With resistance disks of the type hereinafter described, this insulating medium or lining upon the containing Wall must endure Without undue injury a temperature of approximately 2000 degrees F. or more. The function of the tube or retainer is to retain the resistor in position for compression. lit is obvio-us that other than tubular forms of retainers may be employed. Another obvious Way of retaining the plates in their columnar relation is to form the plates With open centers and to string them like beads upon a single rod, the surface of which has been treated previously with a heat-resisting material similar to that employed on the inner suri This is illustrated at 2 in Fig. 6, the resistor being in the form of anface of thev tube.

nular plates 1 strung upon and surrounding the yretaining rod 2. The retainer rod 2 of Fig. 6 may be constructed of a metal rod surfaced with a refractory composition attached to the rod by a layer of cement or vitreous enamel.y

` The resistor in the resistance unit is composed of elements which havebeen described as disks 1. These are graphite disks Which in themselves would be of little value as a resistor, as they possess high conductivity and a low contact resistance. However, they are surrounded or surfaced with a coat-ing or treatment of carbonized coal tar which possesses a comparatively high conductivity and also a higher contact resistance, which can be greatly varied by pressure. Thus there is produced a resistance element of graphite surfaced with carbon, e., consisting of a body of carbon in its form of graphite, surfaced vith carbon in its amorphous form, the carbon skin being the true variable resistance medium and the graphite being merely a suitable conducting support. At the top and bottom of the column of disks are suitable electrodes, or contact parts, for making the electrical connections. A desirable form of electrode is a copper-plated block of graphite having one face left unplated whereby an integral electrode is obtained having a copper face for contact with the metallic leading-in conductor and a graphite face for contact with the resistor strong that there is no appreciable Wear, and

the breakage is negligible with disks of rcasonable thickness.

In resistors of the prior art, using amorphous carbon disks, there is a deterioration as has been pointed out, apparently due to the change of the allotropic state of the carbon. This change may be rapid or slow, according to the severity of' the duty imposed upon the disks. We have found that by using graphite treated as herein described, this deterioration does not occur, and disks may be subjected to very heavy current-carrying duty Without appreciable change throughout long periods of time.

In making the resistor elements of my invention, I use graphite in any suitable state and cut or otherwise form it by any suitable method into the desired shape, Which is preferably that of' a disk. I have found the following process, which I recite in detail, to be Well adapted to the manufacture of my disks: The disks or plates are cutA or savved from rods of artificial graphite and then are ground so that the Hatfaces are parallel. The plates then are placed in'a tray and properly supported so that the flat faces will not make contact with each other. 'This estacas is done in order that the dat aces ali-may' tion in which they are to be placed. Then` they are immersed in a tank containing coal tar thinned by a light oil of the same nature as the tar. The refined coal tar and light oil which we use are obtained as follows: Int-he processes of making gas from coal, there is produced a crude coal tar, which, when refined, yields refined coal tar, light'oil and other substances. lt is the refined coal tar and light oil thus obtained that weV use as a bath in preparing our improved resistance element and our improved resistor. ,The consistency of the tar and oil bath may be varied as desired. The heavier thebathiused, the higher will be the resistance ofthe resulting resistor. During the rst few minutes of immersion the thinning oil enters the plates and leaves a coating of thicktar remaining on the surface, but by the end of about ifteen minutes this sticky coat has been dissolved. After immersion for a sucient length' of time,the`disks and the tar mixture are placed in a centriatugal separator, and if necessary more of the tar mixture is added te insure complete immersion of the disks in the separatori. The surplus tar mixture is thrown from the disks'centrifugally. The

" disks then are-brushed to remove still furvther the adhering tar mixture. 'lhey are then placed in an oven and kept at 66 degrees C. for abouttwenty-*four hours and again are brushed. This gives them a polish and a smooth surface and tends to prevent .i sticking together during further baking.

.-increasin They are then packed in sheet iron tubes, placed in an ovenand baked at4 constantly temperatures-ten hours at 100 degrees ten hours at 150 degrees C., ten

hours at 200 degrees C., ten'hours at 300` degrees C. They are then allowed to cool and are placed in a cast iron retort and are.

L raised to G-degrees C., which causes a complete carbonization of the tar mixture remaining on and in the disks. Upon cooling they are ready :tor use. If', upon inspection, the resistance of any disk should be found too high for the service required, the 4resistance is lowered by grinding the surface of the disk slightly, thus removing a portion of the high-resistance coating which the disk acquires by its. tar treatment. It

i thus may be p aeed in any selected register.

The ability aerded by the foregoing prssef produsse disks "or Plates et varilant resistanees is advantageous that it permits the manufaeture of resistance units adapted for use in circuits of widely different electrical pressures. It is also advantageous in that it permits of a grader tion inthe resistances of the several disks in the saine resistance unit. Such a gradation is sometimes desirable because in resistance units where the column is designed to be held in a vertical position` the weight of the upper disks slightly compresses the lower disks and reduces the resistances of the lower ones. rlhe lower disks therefore may be selected of a higher resistance, and the degree of compression resulting from the weight of the superposed disks will bring this resistance down-to a point where the total resistance of the resistor will be distributed equally throughout its length. Similarly, the gradation or the disks with respect to their resistances may be so made that the disks at the top of the column may have a lower contact resistance per lineal unit than those at the bottom for the purpose of maintaining a uniform temperature along the vertical column of the resistor, this being desirable in that it tends to maintain a constant temperature throughout the length of the tube, the upper portions of the tube naturally tending to be somewhat hotter than the lower, by the rising of the convection currents. rlhe method of `graduating the lineal resistance of the resistor above referred to may be accomplished by varyin the thickness of the disks or plates as wel as by grading their inherent contact resistance, thus accomplishing the result by providing a varying number of contact resistances per lineal unit of column.. When this gradation of resistances along the length of the column is employed, it is advantageous to have some means of designating the order of resistance of the disks in order to facilitate the assembling of the unit and the re-a'ssembling thereof in case the unit is taken apart. This in the case of the disks vof varying thickness is automatically provided. In the case of disks of uniform thickness, the disks may be marked ordesignated in any desired manner.

The life of a carbonaceous resistor under heat is prolonged by excluding air or oxygen from it, and in the device of Fig. l. s eciiic means has been provided to prolong te life of the resistor in this manner. The lower end of the tube is sealed, as shown by the insulating washers and bushing. The top cap 2O seals the upper end of the tube except for the required clearance around the neck of the floating elect-rode or terminal block 16. A considerable degree of isolation for the main cavity of the container is secured by permitting only a tortuous Path 'ance at the neck et the oatf, This is at:

connecting that cavity with the clear:v

tained hy' casting an interns@ downenardl-y.-v

above that shown in the drawings, by providing a number of interleaving tongues.

The neck of. the floating terminal 16 is re-` quired to carry large currents of electricity, yet this neck purposely is made small; This is done in order that a necessary clearance to provide for the sliding of the neck may not result in too` great an opening for the escape or admission of air or gases; also1 in order that sufficient room around the neck may be provided for the 'interleaving flanges above described. The small size of the neck imposes a severe requirement in providing for the connection of the flexible jumper 17. The specific design found to give the best results is shown in section in'Fig. 5. In

this design, the screw-threaded locking bolt j 27 is enlarged at the lower face of its head to'secure a large contact surface With the jumper 17, and that face is integral with the metal of the head and body of the screw, thus forming a conductor of low resistance into the neck of the oating terminal 16. A Washer 26 provides a backing for jumper .17 under pressure of screw-stud 27 but this under surface is not made integral with the part 16 nor is the upper end ofthe neck of that part enlarged to secure greater surface of contact, because then the part would ii'otI pass through the opening inside the flange 20. The cap 20 is cast, and the protecting` extension 17 is bent upward and aroun the flexible jumper 17 to protect that part from accidental injury. `While We have outlined in 'this specification' with considerable detail the structural features and process of manufacture vvhich We have foundto be successful, We do not Wish to be limited in our claims to the exact details specified, as it is obvious that changes might be made Within the skill .of one .versed in the arts Without departing from the:

spirit of our invention.

'While We have referred in the specifica- .tion'and the following claims Yto a col-V 55 umn of disks, We do not Wish to -be confined bythis expression to a vertical pile, as, obviously, the axis of the mass of disks may be disposed vertically, horizontally, or in any intermediate position.

What We claim as new and desire to secure by United States Letters Patentis:

1. The combination of-a variable resistance medium A"surrounding a core of high conductivity, saidiesis'tance,medium bei formed supported uponfthe I,surface and Losanna Within the pore'snear lthe surface' ofsaid core.

' 2; The combination of a orous core of high conductivity and a' sur ace coating 'of carbonized coaltar.Y

3. The combination of a graphite core-.of high conductivity and a surface coating of carbonized coal tar.

4. A resistance unit comprising a column of graphite plates, each having contact surfaces of amorphous carbon. Y

5. A graphite resistance element having an amorphous carbonized surface.

6. The process of making an electrical resistor which comprises forming graphite to the desired shape and coating the surface with carbonaceous material.

7. The process of making an electrical resistor which comprises forming a conductork to the desired shape and treating the conductor with a carbonaceous material, and subsequently heating said carbonaceous m'aterial to produce a contact surface of relatively high resistance.

8. The process of making an electrical resistor which comprises forming graphite to thedesired shape and coating the surface with a carbonaceous material, and subsequently carbonizing said carbonaceous material.

9. The process of making an electrical-re-' sistorI which comprises forming graphite to the desired: shape and coating the surface with coal tar, and subsequently carbonizng said coalt'ar at high temperatures.

10. In a resistance unit a resistor lcoiisisting of a column of graphite disks, .each disk being surfaced with a carbonized substance.

11. A -resistance unit, comprising a, column of porous disks,'each having a sur-.

face coatingl f carbonized coal tar.

12. a resistance element: a graphite body havinga Vcarbonized surface.

- 13. rA resistor comprising a number of compressible disks arranged upon each other in a vertical column-and subject to reduction of resistance by compression, said disks being of varying degrees ofresistanceand arranged with the` disks of higher resistance at the bottom of the column.

14. A resistor comprising a numher-zof' compressible separate contact elements arranged upon each other in a vertical and :subject to reduction of contact-resistance by compression, said disks being of varying degrees of contact 'resistance land arranged with' elements of higher -coitact resistance at the `bottom of thecolumn.- 1

15. In-a'resistanec unit, a container consisting ofa metal tube lined witha'refrac'- tory compound attached to. the tube withfa cement which becomes' plastic with' heat; and a resistor Within saidcontainer. consisting of a series of conducting disks, each surfaced 'With a substancehavingahigh contact resistance variable by pressure, the disks varying among themselves and the disks of the higher resistances being arranged at the bottom of the resistor.

16. In a resistance unit,- a container consisting of a vertical tube and a resistor within said tube consisting cfa series bf conducting disks, each surfaced with a substance having a high contact resistance variable by pressure, the disks varying among themselves, and the disks of the higher resistance being arranged at the bottom of the resistor.

17. ln a resistance unit, a vertical container; and a resistor within said container consisting of a series of graphite disks, each surfaced with a substance having a high contact resistance variable by pressure, the disks varying among themselves, and the disks of the higher resistances being arranged at the bottom of the resistor.

18. In a variable compressible resistance unit,.a vertical series of resistance sub-units of graduated resistances, graduated in resistance with the sub-units of higher resistance at the bottom.

19. In a resistance unit, a chamber; a pressible resistor within said chamber; a oating electrode for said resistor and projecting through one end of said chamber; and a seal for said chamber comprising interleaving annular flanges upon the inner surface of the end of said chamber and upon the contiguous face of said oating electrode.

20. In a resistance unit, a containing chamber; a 'fixed closure therefor; a compressible resistor within said chamber; a movable electrode for said resistor; a stud upon said movable electrode and projecting through said first closure; and interleaving annular fianges surrounding said stud and upon said closure and said electrode whereby a tortuous path is provided between the cavity of said chamber andthe outer air.

21. In a resistance unit, a containing chamber; a fixed closure therefor; a compressible resistor within said chamber; a

movable electrode for said resistor; a studupon said movable electr'ode and project-ing through said fixed closure; an internal flange upon said Xed closure and surroundin said stud, and a flange upon said movab e electrode and surrounding the flange of said fixed closure.

22. In a resistance unit, a terminal comprising a cylindrical stud; and screwthreaded into the end of said stud and occu-\ pyng a major portion of the gross crosssectional area of said stud; a head for said screw having an enlarged under surface for contact; and a flexible ribbon conductor clamped between said surface for contact and a washersupported upon the 'end of said stud.

23. A resistor comprising a number of resistance elements arranged vertically, the resistance value per unit of length of rcsistor being greater -near the bottom of the column than near the top.

24. A compressible resistor, comprising a number of resistance elements having contact resistance variable by pressure and arranged vertically, th`e resistance value per unit of length of resistor being greater near the bottom of the column than near the top.

25. ln a resistance unit, a compressible resistor consisting of separate resistance elements, each having a core of high conductivity and a surface coating of relatively low conductivity.

26. The process of making an electrical resistor element comprising forming a conductor to the desired shape, treating the surface with Huid carbinaceous material, and carbonizing said material.

27. rlfhe process of preparing resistant material, consisting inimpregnating substantially pure graphite in its solid form with a stable, refractory substance of lower electrical conductivity than the graphite.

28. The process of preparing resistant material, consisting in impregnating a block of graphite with a material yielding a stable, refractory substance of lower electrical conductivity than the graphite, and then converting said material into said stable, refractory substance.

29. The process of preparing resistant material, consisting in first impregnating a block of graphite with a material yielding a stable, refractory substance of lower electrical conductivity than the graphite, and then subjecting the impregnated graphite to heat.

30. The process of preparing resistant materia-l, consisting in first impregnating a block of graphite with a mixture comprising a suitable fluid medium and a material lyielding a stable, refractory substance of lower electrical conductivity than the graphite, then raising the impregnated graphite to a temperature sufficient to convert said material into sai-d stable, refractory substance.

31. The process of preparing resistant material, consisting in rst impregnating a block of graphite with a mixture comprising a suitable liuid medium, and a substance yielding a stable, refractory residue of lower electrical conductivity than the graphite and thenl subjecting the impregnated graphite to heat.

32. The process of preparing resistant material, -consisting in first soaking a block of graphite in a solution comprising a suitable solvent and a carbonaceousl substance of lower electrical conductivity than the graphite to introduce said solution into the pores or interstices of said ra bite then ralsinof the soaked graphite to a temperature suicient to volatilize the solvent and to carbonize the substance introduced therein.

33. The process of preparing resistant inaterial, said process consisting in irstfdissolving tar in a suitable solvent, then soaking a block of substantially pure graphite in the solution, and then subjecting the soaked graphite to al temperature suicient to convert the impregnating material into a stable, refractory substance of lower electrical conductivity than the unimpregnated graphite.

34. As a new article of manufacture,the herein described product consisting of a solid, porous block of substantially pure, uncemented carbon, impregnated with a substance of lower elect-rical conductivity and characterized by increased weight and lower electrical conductivity as compared with untreated carbon.

35. As a new article of manufacture, the herein described product consisting of a block of substantially pure graphite in solid form, impregnated with a substance of lower electrical conductivity than the graphite and characterized by a lower electrical conductivity as compared with untreated graphite.

36. As a new article of manufacture, the herein described product, consisting of a block of substantially pure graphite in solid form, impregnated with a stable, refractory substance and characterized by increased weight and lower electrical conductivity as compared with untreated graphite. f v

37. As a new article of manufacture, the herein described product, consisting of a block of substantially pure graphite in solid form, impregnated with a substance of lower electrical conductivity than the graphite and characterized by increased weight and lower electrical conductivity, as com# pared with untreated graphite.

38. As a new article of manufacture, the herein described product, consisting of a block of substantially pure graphite in solid formyimpregnated with a stable, refractory substance of lower electrical Aconductivity than thegraphite and characterized by in creased weight and lower electrical conductivity as compared with untreated graphite.

39. As a new article of manufacture, the

herein described product, consisting of a block of substantial-1y pure graphite in solid form, impregnated with carbon and characterized by increased weight and lower electrical conductivity as compared with untreated graphite.

Signed by us at Muskegon, county of Muskegon and State of Michigan, in the presence of two witnesses.

Witnesses:

JOHN VANDERWERr, Josu: VANDERWERP. 

